Uncover the mystery that lies within the unknown depths

Having the JSON data below:

var lists = [{
        "listId": 1,
        "permission": "WRITE"
    }, {
        "listId": 2,
        "permission": "WRITE"
    }, {
        "listId": 2,
        "permission": "READ"
    }, {
        "listId": 3,
        "permission": "READ"
    }, {
        "listId": 3,
        "permission": "WRITE"
    }, {
        "listId": 5,
        "permission": "WRITE"
    }]

As well as this one:

var arr = [{
    "listId": 1,
    "confidentiality": "PUBLIC",
    "listName": "List name here..1",
    "permission": "WRITE"
}, {
    "listId": 2,
    "confidentiality": "PUBLIC",
    "listName": "List name here..2",
    "permission": "READ"
}, {
    "listId": 3,
    "confidentiality": "CONFIDENTIAL",
    "listName": "List name here..3",
    "permission": "WRITE"
}, {
    "listId": 4,
    "confidentiality": "CONFIDENTIAL",
    "listName": "List name here..4",
    "permission": "WRITE"
}, {
    "listId": 5,
    "confidentiality": "CONFIDENTIAL",
    "listName": "List name here..5",
    "permission": "WRITE"
}]

The task at hand is to filter data from arr and push it to results[] if there is a match in listId and permission within lists[...].

var result = [];

for(var i = 0; i < arr.length; i++) {   
  for(var j = 0; j < lists.length; j++) {     
     if( (arr[j].listId == lists[i].listId) && (arr[j].permission == lists[i].permission) ) {
        result.push(arr[j]);
     }
  }
}
console.log(result);

The issue arises when I encounter listId undefined if arr.length is smaller than lists.length.

Any suggestions on how to tackle this problem?

javascriptfor-loop

Answer №1

If the length of arr is smaller than lists, I encounter an issue where listId becomes undefined

To resolve this problem, ensure that you are using the correct indexes for each array - use i for arr and j for lists

if( (arr[i].listId == lists[j].listId) && (arr[i].permission == lists[j].permission) )

Answer №2

A potential optimization could involve restructuring the code to utilize a lookup table for permissions, streamlining the process by employing just a single loop to handle the result set.

var lists = [{ listId: 1, permission: "WRITE" }, { listId: 2, permission: "WRITE" }, { listId: 2, permission: "READ" }, { listId: 3, permission: "READ" }, { listId: 3, permission: "WRITE" }, { listId: 5, permission: "WRITE" }],
    array = [{ listId: 1, confidentiality: "PUBLIC", listName: "List name here..1", permission: "WRITE" }, { listId: 2, confidentiality: "PUBLIC", listName: "List name here..2", permission: "READ" }, { listId: 3, confidentiality: "CONFIDENTIAL", listName: "List name here..3", permission: "WRITE" }, { listId: 4, confidentiality: "CONFIDENTIAL", listName: "List name here..4", permission: "WRITE" }, { listId: 5, confidentiality: "CONFIDENTIAL", listName: "List name here..5", permission: "WRITE" }],
    permissions = {},
    result;

lists.forEach(function (p) {
    permissions[p.listId] = permissions[p.listId] || {};
    permissions[p.listId][p.permission] = true;
});

result = array.filter(function (a) {
    return permissions[a.listId] && permissions[a.listId][a.permission];
});

console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

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